1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device having driver circuits each for driving a bus, a clock line or an input/output line of a semiconductor chip.
2. Description of the Prior Art
The power consumption of a CMOS circuit can be given by the following formula: EQU P=pt.multidot.f.multidot.CL.multidot.Vs.multidot.V.sub.DD (1)
where Vs denotes the signal amplitude; V.sub.DD denotes the supply voltage; pt denotes the switching probability; f denote the clock frequency; and CL denotes the load capacitance.
In the ordinary circuit, conventionally since the amplitude of the signal changes between the supply voltage and the ground voltage, the above formula (1) can be expressed as EQU P=pt.multidot.f.multidot.CL.multidot.V.sub.DD.sup.2 (2)
In the ordinary CMOS circuit, however, since there exist relatively large parasitic capacitances in the bus and clock line, or the input/output line of the semiconductor chip, the driver circuits for driving these lines consume a relatively large power, respectively. Recently, therefore, a lower power consumption has been required more and more for the semiconductor integrated circuit device, so that this problem has become an important problem to be solved.
By the way, as understood on the basis of the above formula (1), one of the methods of reducing the power consumption is to reduce the signal amplitude. However, this method is not easy. The reasons are as follows: first, it is difficult to realize the driver circuit for outputting a small amplitude signal under a low power consumption. Or else, it is difficult to realize a receiver circuit for receiving the small-amplitude signal and returning the received small-amplitude signal to the ordinary amplitude signal under a low power consumption.
In addition, in the case of the small-amplitude signal, since the margin against noise is inevitably reduced, it is difficult to prevent erroneous signals from being transmitted. In particular, in the case of the input/output line of the chip, since the signal is susceptible to an influence of signal reflection, there exists a problem of cross talk with the ordinary signals.
Further, there exists a problem of the threshold fluctuations of the receiver circuit due to the change of temperature and the dispersion of device characteristics.
For the reasons as described above, the small-amplitude signals have been so far used for only a part of the circuits whose characteristics are well known (e.g., as with the case of bit line signals of a memory device). In the ordinary semiconductor circuit device, on the other hand, the signals having an amplitude changing between the supply voltage and the ground voltage have been so far used. As a result, there exists a problem in that the power consumption cannot be reduced in the semiconductor integrated circuit device having the driver circuits.